Lyme disease has recently emerged as the most prevalent vector-borne illness in the United States, and evidence suggests that its distribution is continuing to expand. Ixodes dammini, the sole vector of importance in northeastern U.S., is widely but patchily distributed in parts of the region. During the past 2 decades, the range of I. dammini and Lyme disease has spread to encompass much of the coastal northeast; enigmatically, movement inland has been slow and spatially variable. Neither low frequency of new tick introductions nor unavailability of appropriate vertebrate hosts can adequately explain why this vector has not more rapidly invaded certain regions. We propose to use laboratory and field experiments, and a novel technique for modeling and analysis of spatial relations termed Geographical Information Systems (GIS), to determine how non-host, environmental factors influence the survival and limit the range of I. dammini in the northeastern U.S. Specifically, we shall determine I. dammini abundances throughout the states of Connecticut and Massachusetts by sampling ticks on hunter-killed white-tailed deer, and calculating variation in tick abundances over the entire region of both states. These results will be integrated with the spatial distributions of climatic, vegetation, soil, altitude and other environmental data from the same areas. Using GIS, we will analyze the environmental determinants of this tick's macrogeographic distribution, and model the rate and direction of its spread. Other laboratory and field studies will examine the effects of various microclimatic conditions on the off-host survival of coastal northeastern and northern mid-western populations of I. dammini. Microgeographic variation in I. dammini abundance will be evaluated in relation to microclimate and vegetation, while controlling for habitat use by radio-collared deer. The long-term impact of habitat manipulation on I. dammini abundance will be studied by various experiments that may be useful in local tick control efforts. Our ultimate goal is to determine the environmental conditions that presently limit the distribution of I. dammini, where and at what rate new infestations might be anticipated, and how the impact on public health resulting from the expanding range of this Lyme disease vector may be lessened.